It is not possible to pre-book individual pitches but you can book pitch type, ie awning, non-awning or serviced pitch.

I can only assume the pitches you were hoping to move to were of a different type which could mean that, if you occupied one, there would not be a pitch available for someone who had booked that type. 

I've heard that the nearby site is good. Give it a try next time.

With respect, nobody 'parked you' anywhere, you chose the pitch?

As tin wheeler says, you just cannot book a specific pitch, pitch type yes but not a certain pitch.

Had you read all about Henley then you would have realised the road can get noisy.

I take it you were on a standard pitch with awning (white peg)and was it the reason you "think" others had booked pitches was that the "empty pitches"were standard pitches without awning(blue pegs) which looking at the site map seem more are away from the road?